The present disclosure relates to hydraulic devices having a discharge valve, and more particularly to hydraulic devices for vehicles that are moved by an engine.
Conventionally, a hydraulic device is proposed which is mounted on an automobile having an idling stop function and which includes a mechanical pump that is operated by power of an engine, an electromagnetic pump that is driven by electric power, a linear solenoid valve SL1 that regulates a discharge pressure from the mechanical pump, and a switching valve that is operated by an oil pressure (modulator pressure) from the mechanical pump to switch an supply pressure to a hydraulic servo for a C1 clutch that is to be engaged when the automobile is started to either an output pressure (regulated pressure) from the linear solenoid valve or a discharge pressure of the electromagnetic pump. The switching valve includes a drain port that directs an oil pressure from the electromagnetic pump to a check valve (discharge valve), in addition to a first input port that communicates with the linear solenoid valve, a second input port that communicates with the electromagnetic pump, and an output port that communicates with the hydraulic servo for the C1 clutch (see Japanese Patent Application Publication No. 2012-122560).
When the engine is rotated in a D range, the modulator pressure based on the mechanical pump is applied to a spool of the switching valve. The switching valve is thus switched to a first state where the first input port communicates with the output port, and the regulated pressure from the linear solenoid valve based on the mechanical pump is supplied to the hydraulic servo for the C1 clutch. In an idling stop state, the mechanical pump is stopped, and no modulator pressure is generated. The switching valve is thus switched to a second state where the second input port communicates with the output port. A predetermined oil pressure (stroke end pressure) from the electromagnetic pump that is driven in the idling stop state is supplied to the hydraulic servo for the C1 clutch, and this hydraulic servo is maintained in the state immediately before the C1 clutch is engaged, preparing for the automobile to be started again.
The check valve (discharge valve) having an increased opening pressure communicates with the drain port of the switching valve. In the first state, the drain port communicates with the electromagnetic pump. The switching valve causes leakage of an oil pressure into the input ports from between a valve body and a spool.
In the first state where the oil pressure based on the mechanical pump is supplied to the hydraulic servo for the C1 clutch, the oil pressure due to the leakage is applied from the first input port to an oil pressure supply oil passage of the electromagnetic pump. Since this oil passage communicates with the check valve via the drain port, the oil pressure in this oil passage is maintained at a set pressure of the check valve with the increased opening pressure, and is prevented from increasing to an excessive level.
A motor-driven pump that is driven by an electric motor may be used instead of the electromagnetic pump. Electrically driven pumps including the electromagnetic pump and the motor-driven pump are herein defined as electric pumps.